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C------------------------------------------------------------------------------
subroutine ftxypx(xpos,ypos,xref,yref,xrefpix,yrefpix,
& xinc,yinc,rot,type,xpix,ypix,status)
C Fortran version of worldpos.c -- WCS Algorithms from Classic AIPS
C Translated by James Kent Blackburn -- HEASARC/GSFC/NASA -- November 1994
C routine to determine accurate pixel coordinates from an RA and Dec
C does: -SIN, -TAN, -ARC, -NCP, -GLS, -MER, -AIT projections
C returns 0 = good,
C 501 = angle too large for projection;
C 502 = bad values
C 503 = ???undocumented error - looks like an underflow???
C Input:
C dbl xpos x (RA) coordinate (deg)
C dbl ypos y (dec) coordinate (deg)
C dbl xref x reference coordinate value (deg)
C dbl yref y reference coordinate value (deg)
C dbl xrefpix x reference pixel
C dbl yrefpix y reference pixel
C dbl xinc x coordinate increment (deg)
C dbl yinc y coordinate increment (deg)
C dbl rot rotation (deg) (from N through E)
C chr type projection type code e.g. "-SIN"
C Output:
C dbl xpix x pixel number (RA or long without rotation)
C dbl ypiy y pixel number (dec or lat without rotation)
C int status error status flag, zero
integer status
double precision xpos,ypos,xref,yref,xrefpix,yrefpix
double precision xinc,yinc,rot,xpix,ypix
character*(*) type
integer error1,error2,error3,error4
parameter (error1=501)
parameter (error2=502)
parameter (error3=503)
parameter (error4=504)
double precision dx,dy,dz,r,ra0,dec0,ra,dec
double precision coss,sins,dt,da,dd,sint,oldxpos
double precision l,m,geo1,geo2,geo3,sinr,cosr
double precision cond2r
parameter (cond2r=1.745329252d-2)
double precision twopi,deps
parameter (twopi = 6.28318530717959)
parameter (deps = 1.0d-5)
integer i,itype
character*4 ctypes(8)
data ctypes/ '-SIN', '-TAN', '-ARC', '-NCP',
& '-GLS', '-MER', '-AIT', '-STG' /
if (status .gt. 0) return
C *** 0 hour wrap around test
oldxpos = xpos
dt = (xpos - xref)
if (dt .gt. +180) xpos = xpos - 360
if (dt .lt. -180) xpos = xpos + 360
C *** Default values - Linear
dx = xpos - xref
dy = ypos - yref
dz = 0.0
C *** Correct for rotation
r = rot * cond2r
cosr = dcos(r)
sinr = dsin(r)
dz = dx * cosr + dy * sinr
dy = dy * cosr - dx * sinr
dx = dz
C *** Check axis increments - bail out if either 0
if ((xinc .eq. 0.0) .or. (yinc .eq. 0.0)) then
xpix = 0.0
ypix = 0.0
status = error2
goto 30
end if
xpix = dx / xinc + xrefpix
ypix = dy / yinc + yrefpix
C *** Find type of coordinate transformation (0 is linear)
itype = 0
do 10 i = 1, 8
if (ctypes(i) .eq. type) itype = i
10 continue
C *** Done if linear
if (itype .eq. 0) goto 30
C *** Non-Linear position
ra0 = xref * cond2r
dec0 = yref * cond2r
ra = xpos * cond2r
dec = ypos * cond2r
C *** Compute directional cosine
coss = dcos(dec)
sins = dsin(dec)
l = dsin(ra-ra0) * coss
sint = sins * dsin(dec0) + coss * dcos(dec0) * dcos(ra-ra0)
C *** Process by case
if (itype .eq. 1) then
C *** SINE from '-SIN' type
if (sint .lt. 0.0) then
status = error1
goto 30
end if
m = sins * dcos(dec0) - coss * dsin(dec0) * dcos(ra-ra0)
else if (itype .eq. 2) then
C *** TANGENT from '-TAN' type
if (sint .le. 0.0) then
status = error1
goto 30
end if
m = sins * dsin(dec0) + coss * dcos(dec0) * dcos(ra-ra0)
l = l / m
m = (sins*dcos(dec0) - coss*dsin(dec0)*dcos(ra-ra0)) / m
else if (itype .eq. 3) then
C *** Arc from '-ARC' type
m = sins*dsin(dec0) + coss*dcos(dec0)*dcos(ra-ra0)
if (m .lt. -1.0) m = -1.0
if (m .gt. 1.0) m = 1.0
m = dacos(m)
if (m .ne. 0) then
m = m / dsin(m)
else
m = 1.0
end if
l = l * m
m = (sins*dcos(dec0) - coss*dsin(dec0)*dcos(ra-ra0)) * m
else if (itype .eq. 4) then
C *** North Celestial Pole from '-NCP' type
if (dec0 .eq. 0.0) then
status = error1
goto 30
else
m = (dcos(dec0) - coss * dcos(ra-ra0)) / dsin(dec0)
end if
else if (itype .eq. 5) then
C *** Global Sinusoid from '-GLS' type
dt = ra - ra0
if (dabs(dec) .gt. twopi/4.0) then
status = error1
goto 30
end if
if (dabs(dec0) .gt. twopi/4.0) then
status = error1
goto 30
end if
m = dec - dec0
l = dt * coss
else if (itype .eq. 6) then
C *** Mercator from '-MER' type
dt = yinc * cosr + xinc * sinr
if (dt .eq. 0.0) dt = 1.0
dy = (yref/2.0 + 45.0) * cond2r
dx = dy + dt / 2.0 * cond2r
dy = dlog(dtan(dy))
dx = dlog(dtan (dx))
geo2 = dt * cond2r / (dx - dy)
geo3 = geo2 * dy
geo1 = cos (yref * cond2r)
if (geo1 .le. 0.0) geo1 = 1.0
dt = ra - ra0
l = geo1 * dt
dt = dec / 2.0 + twopi / 8.0
dt = dtan(dt)
if (dt .lt. deps) then
status = error2
goto 30
end if
m = geo2 * dlog(dt) - geo3
else if (itype .eq. 7) then
C *** Aitoff from '-AIT' type
l = 0.0
m = 0.0
da = (ra - ra0) / 2.0
if (dabs(da) .gt. twopi/4.0) then
status = error1
goto 30
end if
dt = yinc * cosr + xinc * sinr
if (dt .eq. 0.0) dt = 1.0
dt = dt * cond2r
dy = yref * cond2r
dx = dsin(dy+dt)/dsqrt((1.0+dcos(dy+dt))/2.0) -
& dsin(dy)/dsqrt((1.0+dcos(dy))/2.0)
if (dx .eq. 0.0) dx = 1.0
geo2 = dt / dx
dt = xinc * cosr - yinc * sinr
if (dt .eq. 0.0) dt = 1.0
dt = dt * cond2r
dx = 2.0 * dcos(dy) * dsin(dt/2.0)
if (dx .eq. 0.0) dx = 1.0
geo1 = dt*dsqrt((1.0+dcos(dy)*dcos(dt/2.0))/2.0)/dx
geo3 = geo2 * dsin(dy) / dsqrt((1.0+dcos(dy))/2.0)
dt = dsqrt ((1.0 + dcos(dec) * dcos(da))/2.0)
if (dabs(dt) .lt. deps) then
status = error3
goto 30
end if
l = 2.0 * geo1 * dcos(dec) * dsin(da) / dt
m = geo2 * dsin(dec) / dt - geo3
else if (itype .eq. 8) then
C *** Stereographic from '-STG' type
da = ra - ra0
if (dabs(dec) .gt. twopi/4.0) then
status = error1
goto 30
end if
dd = 1.0 + sins*dsin(dec0) + coss*dcos(dec0)*dcos(da)
if (dabs(dd) .lt. deps) then
status = error1
goto 30
end if
dd = 2.0 / dd
l = l * dd
m = dd * (sins*dcos(dec0) - coss*dsin(dec0)*dcos(da))
else
C *** Unsupported Projection
status = error4
goto 30
end if
C *** Convert back to degrees
dx = l / cond2r
dy = m / cond2r
C *** Correct for rotation
dz = dx * cosr + dy * sinr
dy = dy * cosr - dx * sinr
dx = dz
C *** Convert to PIXELS ... yeah!
xpix = dx / xinc + xrefpix
ypix = dy / yinc + yrefpix
30 continue
C *** reset xpos to correct for in place modification
xpos = oldxpos
end
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